A subscription In-App purchase shares attributes of both consumable and non-consumable products. Like a consumable product, a subscription may be purchased multiple times and you can implement your own renewal mechanism in your app. However, subscriptions must be provided on all devices associated with a user.
Here developer will have to deliver subscriptions through their own server. Developer should also handle subscriptions across multiple devices.

There are 2 types of subscription In-App purchases

Auto-renewable Subscriptions

An auto-renewable In-App Purchase subscription allows the user to purchase in-app content for a set duration of time. At the end of that duration the subscription will renew itself, unless the user opts out, which he/she has to do from his/her account in iTunes.

Non-renewing Subscriptions
A Non-renewing subscription do not have the feature where we can set the duration we want to offer for our In-App purchase. So we must provide the information some other way. It requires a user to renew each time and the expiry of the subscription should be handled by the developer.